The invention relates to the radio communication system, particularly effective technique applied to the radio communication system such as the wireless LAN (Local Area Network).
In a wireless communication system using a wireless communication technique such as a wireless LAN, constituted by a plurality of base transceiver stations (BTS) and a plurality of wireless system terminals, a wireless system terminal selects a base transceiver station with a highest receiving signal strength as a connecting destination. The receiving signal strength of the wireless system terminal changes incessantly. Thus, if a plurality of base transceiver stations having the same receiving signal strength is present, the wireless system terminal switches connection to a base transceiver station with the highest receiving signal strength one after another. This phenomenon is referred to as roaming. In order to perform this roaming, both of the base transceiver stations and the wireless system terminals allocate enormous computational resources to processing for switching a connecting destination. For this reason, communication throughput between the wireless system terminals and the base transceiver stations in the wireless communication system is reduced. Further, if most of the wireless system terminals in the system are connected to the base transceiver station with the highest receiving signal strength in unison, communication loads are concentrated onto one base transceiver station. Hence, the waiting periods of the wireless system terminals for communication sometimes become extremely extended.
Even if a lot of base transceiver stations are disposed, the throughput of the overall system will not be improved if communication is concentrated onto some of the base transceiver stations. It is thus necessary to evenly distribute communication loads throughout the base transceiver stations. However, in a method where wireless system terminals are dynamically assigned to base transceiver stations with low communication loads, it sometimes become necessary to perform a lot of processing for switching the connecting destination, thereby reducing the throughput. On the other hand, assume that the number of connected stations is just balanced. Then, even if 10 wireless system terminals are connected to each of two base transceiver stations, communication load balance cannot be achieved if wireless system terminals with large communication amounts are concentrated onto one base transceiver station and wireless system terminals with small communication amounts are concentrated on another base transceiver station.
The following are the more specific, conventional methods of reducing the frequency of roaming of a wireless system terminal and achieving communication load balance:
(1) Communication Load Monitoring Method
In this method, the wireless system terminal monitors communication loads on the respective base transceiver stations. When the communication load on the base transceiver station to which the wireless system terminal is connected has increased, roaming to other base transceiver station with a lower communication load is performed.
(2) Method of Checking Number of Connected Wireless System Terminals
Before establishing connection, the wireless system terminal inquires of the respective base transceiver stations the number of wireless system terminals connected thereto, and is connected to the base transceiver station with the smallest number of wireless system terminals connected thereto. When the receiving signal strength of the connected base transceiver station has been reduced, roaming to other wireless base station with a higher receiving signal strength is performed as necessary.
(3) Connecting Destination Registration Method
A single base transceiver station is registered in the wireless system terminal as a connecting destination, so that the connecting destination is fixed at one station, thereby disabling roaming. The number of wireless system terminals connected is thereby balanced artificially.